1. Field of the Invention
The present invention relates to a dental automatic cutting apparatus that is used for preparing, through cutting processing, dental prostheses for undergoing prosthesis of missing teeth in an oral cavity of a patient, such as crowns and inlays, and particularly, to a dental automatic cutting apparatus in which a tool cassette accommodating plural kinds of and/or a plural number of cutting tools is detachable in a desired position.
2. Description of the Related Art
Dental prostheses for undergoing prosthesis of missing teeth in an oral cavity of a patient, such as crowns and inlays (the dental prosthesis or prostheses being sometimes referred to simply as xe2x80x9cprosthesisxe2x80x9d or xe2x80x9cprosthesesxe2x80x9d, hereinafter), are required to have a severe fitting precision. Accordingly, it has hitherto been commonly employed to prepare the prostheses by a precision casting process such as a lost wax process. Further, during the preparation of these prostheses, it was considered to be necessary to take a number of steps starting from preparation of a cavity as a prosthetic part by a dentist and inclusive of impression taking (molding) of the missing part and preparation of a gypsum model. Moreover, since, as described above, a severe fitting precision is required for the preparation of the prostheses, it is legally regulated within Japan that a person having a national qualification, called as a dental technician, must deal with it.
Now, with the progress of a computer technology in recent years, processing technologies with the computer technology as a nucleus are developing in various fashions. Such technologies are a processing technology generally called as CAD (computer aided design) and CAM (computer aided manufacturing). The application of the processing technology by CAD/CAM is being also attempted in various objects for preparing such prostheses in the dental field as described above.
For example, the technology as disclosed in Japanese Patent Laid-Open No. 187802/1983 is one example thereof, and the disclosed technology includes contents called as a digital type processing process by computer control. Specifically, this technology is concerned with a technology in which, by using a non-contact type reader utilizing a light wave or an acoustic wave, a shape of the prosthesis is read, the obtained data are converted into a digital signal, the signal is then sent to a digital control type machine tool, thereby preparing a prosthesis that is precisely fitting to the subjected body part (prosthetic part). These matters are automatically effected by a computer.
As the digital control type machine tool as exemplified herein, a micro slicing machine can be exemplified. As devices that can be used for processing small workpieces required to have a high precision, such as prostheses, a group of machine tools generally called as a machining center (the digital control type machine tool being sometimes referred to simply as xe2x80x9cprocessing apparatusxe2x80x9d, hereinafter) is being used with the progress of machine tools in recent years.
Under such circumstances, in order to prepare effectively prostheses having a high precision, various devices have been attempted with respect to the mechanism of the apparatus itself as well as the material subjected to the cutting processing and cutting tools. For example, as a device for the processing apparatus itself, there is an application to a small-sized processing apparatus with an automatic opening and closing mechanism using a compressed air of a spindle chuck. Hitherto, the automatic opening and closing mechanism using a compressed air of a spindle chuck gripping a cutting tool could be installed only in a large-sized processing apparatus because of complexity of its construction. However, by applying various devices, it has become possible to install it even in a small-sized apparatus.
Further, an object for performing the preparation of a prosthesis by CAD/CAM resides in the matter that prostheses having a high dimensional precision as a single product are respectively prepared so as to be fitting to the shape of a part to be installed (a missing tooth of a patient) and that a large number of prostheses having various shapes can be continuously and simply prepared without giving troubles. In order to achieve this object, with respect to the material, a semi-product close to the shape and size of a prosthesis to be prepared, for example, one having a shape of column or rectangle (such semi-product being sometimes referred to simply as xe2x80x9csemi-productxe2x80x9d, hereinafter), is prepared in advance.
And, examples of materials for the semi-product include from relatively soft ones such as dental noble metal alloys to rigid ones such as dental titanium alloys as well as from molded ones with a relatively good precision, which can be readily cut, such as dental synthetic resins (generally called as xe2x80x9cdental composite resinsxe2x80x9d but sometimes called simply as xe2x80x9cresinsxe2x80x9d) to ones that are relatively inaccurate in size because of their properties and are hardly subjected to cutting processing, such as dental ceramics.
Now, under conditions in which such various materials are used as the semi-product, in order to subject the semi-product to cutting processing into a prosthesis having a desired shape, a processing in which by gripping a cutting tool at the tip of a spindle, shaping is carried out by rotating cutting is generally employed. For this purpose, it is a necessary condition for performing the processing with a good efficiency and a high precision that the cutting contents are previously designed and that cutting tools suitable for the cutting contents are prepared. This is because there is a background that because of differences in rough cutting or finish cutting fine cutting) or the like in terms of the cutting contents, differences in hardness due to a difference of the material, and deterioration in sharpness of a cutting edge of the cutting tools caused by cutting a number of semi-products, it is necessary to appropriately exchange the cutting tool from the standpoints to maintain processing efficiency and processing precision.
In this connection, the cutting tools used in the dental CAD/CAM will be described below in a little more detail. For the dental ceramics or dental composite resins to be used as a prosthetic material, use of a diamond cutter is preferred; and for processing of dental metals, particularly processing of dental titanium alloys, use of a carbide cutter is preferred. And, for example, when one wishes to obtain a whole of a part corresponding to an upper portion of a tooth (such a processed material being sometimes referred to simply as xe2x80x9ccrownxe2x80x9d, hereinafter) as a prosthesis through processing, while gripping the cutting tools, he or she must selectively use some cutting tools among those having different tip sizes and shapes as prepared taking into consideration purposes.
With respect to the prosthesis, in the case of the above-described crown, there are two types of those for a posterior tooth and an anterior tooth. On the other hand, there is also a prosthesis called as xe2x80x9cinlayxe2x80x9d, which is used for filling a cavity formed by cutting off a tooth portion where a dental caries has been generated. The inlay includes a number of variations in terms of the size and shape such that it is not too much to say that there is nothing at all that has the same size and shape. In order to subject such an inlay to processing with a good precision, one must previously choose cutting tools having a size and a shape suitable for a shape to be cut. The thus previously chosen cutting tools are gripped by a chuck provided in a spindle and fixed by an operator personally in accordance with the progress of the cutting works.
However, if the cutting tools are replaced manually one by one, even when the automatic cutting processing is realized expressly by computer control, the working is interrupted on each occasion. Accordingly, not only the cutting works are inefficient, but also the complication for a worker is not solved. Thus, it is hard to say that benefits by the computer control are thoroughly utilized.
In order to overcome such inefficient and complicated matters, it may be considered to align a spindle for gripping a necessary number of cutting tools as expected. In other words, by employing such construction, cutting tools each having a size and a shape as expected are first set (gripped) in respective spindles and left to the automatic control by a computer until the completion of cutting. In this case, since the cutting works are not interrupted, not only the working efficiency is improved, but also a worker is liberated from the complication in exchange of the cutting tools.
However, the above-described construction involves new problems that not only the apparatus becomes large in size, but also the apparatus cost increases. In other words, if the number of spindles increases, the spindles must be subjected to position fitting, resulting in a non-negligible problem from the viewpoint of precision. And, after all, since it is impossible to use a plurality of spindles at once (the prosthesis is subjected to the processing and is extremely small, and such becomes a bottle-neck), this construction does not contribute to a reduction in the processing time so much. Rather, a risk of accident will increase in proportion to an increase in the number of the constructing members.
Accordingly, it is self-explanatory that when a construction in which at most two spindles are aligned is employed so as to make the whole of the apparatus small in size as far as possible, and the exchange of the cutting tools is automatically carried out by the control of a computer incorporated in the processing apparatus, the workability is largely improved. But, in order to choose suitable cutting tools depending on the progress of the cutting works, not only a vast and complicated program for computer control is necessary, but also a high-level technology for making a machine judge is involved. Accordingly, these requirements cannot be met at a current technical level. Therefore, realization of a processing apparatus in which desired cutting tools are automatically exchanged in a simpler construction and a human help is not substantially required has been demanded.
The present invention is aimed to provide a dental automatic cutting apparatus that is used for preparing dental prostheses such as crowns and inlays in a processing process by CAD/CAM and in which cutting tools are made automatically detachable to a chuck and a tool cassette by automatic control mechanism, wherein a necessary cutting tool is automatically gripped by or taken out from a chuck of a spindle from or to the tool cassette depending on the processing order by automatic control mechanism aligned in the processing apparatus, and the tool cassette set with necessary cutting tools as previously expected can be position-fixed simply and precisely to a predetermined position on the processing apparatus.
We, the present inventors made extensive and intensive investigations in order to overcome the above-described problems of the related art. As a result, we have invented a dental automatic cutting apparatus having a construction in which cutting tools are made automatically detachable to a chuck and a tool cassette by automatic control mechanism comprising: an engagement means provided to the tool cassette and a base block to maintain the tool cassette in a detachable manner to the base block to a desired position relation, the tool cassette provided on its front surface side with at least two post-inserting bores through which each tool post having a function to accommodate and hold the cutting tool which can be inserted, and the base block is fixed to a main body of the dental automatic cutting apparatus; and a connection means for connecting the engagement means is provided in the tool cassette to the base block to fix the tool cassette.
And, the inventors have found that, in the above-described construction, it is preferred that at least one proximity sensor is aligned in a predetermined position on the base block in the side to which the tool cassette is fixed, and the proximity sensor discriminates the type of a signal imparted to the fixed tool cassette; the engagement means is a bore formed by combining a cassette-fixing pin vertically provided on a rear surface side of the tool cassette, a groove bored on an upper surface of the base block, and a groove bored on a lower surface of a cramp block vertically movable against the base block above the base block, the bore being engaged with the cassette-fixing pin, and the connection means has a structure to press the cramp block to the base block side; and that an adjusting screw is aligned for adjusting a distance (gap) between the tool cassette and the base block on the rear surface of the tool cassette and/or on the front surface of the base block.